1. Field of the Invention
The present invention relates to a control system used in a chemical mechanical polishing (CMP) process, and more specifically, to a control system for in-situ feeding back a polish profile.
2. Description of the Prior Art
In the semiconductor industry, a chemical mechanical polishing (CMP) process is one of the most common and important planarization tools applied. For example, the CMP process can be used to remove a topographical target of a thin film layer on a semiconductor wafer. The CMP process produces a wafer with both a regular and planar surface, to ensure an acceptable yield rate in following processes. Certain complications are involved in the CMP process, such as properties of the target thin film layer, uniformity of the target thin film surface, composition and pH value of the slurry, composition of the polishing pad, platen rotational speed, head down force, etc. These factors create difficulty in process control of the CMP process.
Multiple methods are available for determining an endpoint of the CMP process, with the simplest being to control polishing time. However, this method does not account for variation among different wafers, and a sufficient thickness of layer is required to prevent over-polishing. As well, a stop layer is often positioned below the target thin film layer to prevent over-polishing. The removal rate of the stop layer is usually less than that of the overlying target thin film layer. In other words, the removal rate of the target thin film layer is required to be greater than that of the underlying stop layer. The most common method of determining the endpoint of the CMP process is by optically monitoring the dielectric layer by a photo detector. The data, detected by the photo detector, of the intensity of the reflected light beam undergoes periodic changes during the CMP process. A periodically changing curve is thus obtained. Consequently, the endpoint of the CMP process can be precisely determined by using the periodically changing curve.
However, methods provided in the preceding paragraphs are merely used for determining the endpoint of the CMP process. To improve the uniformity of the wafer and increase the product yield rate, it is necessary to provide a method of in-situ feeding back a polish profile during the CMP process.
It is therefore a primary object of the present invention to provide a control system used in a chemical mechanical polishing (CMP) process so as to in-situ feed back a polish profile.
According to the claimed invention, a CMP machine comprises a polish platen, comprising at least a first ring-shaped region and a second ring-shaped region, a polish pad installed on the polish platen, a carrier head, used for holding a wafer and comprising an inner portion and an outer portion respectively corresponding to the first ring-shaped region and the second ring-shaped region, positioned over the polish pad, and a slurry supply device, comprising a first slurry pump valve positioned corresponding to the first ring-shaped region, and a second slurry pump valve positioned corresponding to the second ring-shaped region. A control system for in-situ feeding back a polish profile of the CMP machine comprises a control unit and at least a first sensor and a second sensor. The first and the second sensor are installed in the first and second ring-shaped regions, respectively. The control unit is electrically connected to the first sensor and the second sensor for comparing the polish rate of the wafer over the first ring-shaped region and the polish rate of the wafer over the second ring-shaped region according to signals of the first sensor and the second sensor, and adjusting the amounts of the slurry supplied by the first slurry pump valve and supplied by the second slurry pump valve according to a predetermined process, or adjusting the force loaded by the inner portion of the carrier head and loaded by the outer portion of the carrier head according to the predetermined process.
It is an advantage of the present invention against the prior art that the first sensor and the second sensor are employed to transfer signals of thicknesses of a thin film on portions of the wafer respectively corresponding to the first and the second ring-shaped regions, or those of surface temperatures of portions of the wafer respectively corresponding to the first and the second ring-shaped regions, to the control unit during the CMP process. After calculating the polish rates of the wafer over the first and the second ring-shaped regions, the control unit adjusts the amounts of the slurry supplied by the first and the second slurry pump valves, the forces loaded by the inner and the outer portions of the carrier head, or the heights of the polish platen over the first and the second ring-shaped regions so as to in-situ compensate the polish profile of the wafer. Polishing errors are thus immediately corrected during the CMP process. Consequently, both the uniformity and the yield rate of the product are significantly improved.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings.